Increasing the service life of pellet car grate bars made of 40Х24Н12СЛ steel

Intercrystallite corrosion (ICC) is the main reason to decrease service life of pellet car grate bars made of steel 40Х24Н12СЛ. In the process of the study of microstructure of pellet car grate bars manufactured according to GOST 977–88, the structure defects were established that increase the tendency to ICC. To prevent the ICC of the bars, a mode of heat treatment was elaborated, consisting of two basic operations: air hardening with preliminary exposure within 80 minutes at the temperature 1100 °С, followed by tempering within 150 minutes at the temperature 900 °С. The study of the structure of the pilot grate bar showed that the selected mode of the hardening enables to dissolve the carbide network in the structure of the detail and crash large carbides, and the subsequent tempering contributes to the growth of the carbide phase in the entire volume of metal, partially remaining in the structure after hardening. It was shown that the proposed mode of the heat treatment contributes to bringing the structure of the metal to a more “equilibrium” state, which will allow to exclude the formation of large carbides and carbide network, growth and coagulation along the grain boundary. Results of tests of a pilot batch of grate bars installed at an industrial induration machine with a working area of 768 m2 and operating temperature of 20–1310°С presented. It was established that the elaborated technology ensures absence of casting defects in the grate bars – cracks and warping, inclination of the grate bars to ICC, increased by 23.13% heat resistance compared to the reference grate bars of foreign supply due to the globular form of carbide secretions with a minimum length of borders along which the metal matrix is depleted by chrome. Industrial testing of the grate bars manufactured under the experimental technology has proved the practical significance and applicability of the performed research.